(a) Field of the Invention
The present invention relates a microwave filter, and in detail, relates to a resonator filter using a dielectric material.
(b) Description of the Related Art
A microwave filter selecting a desired frequency band determines performance of a wireless telecommunications system. Especially, when the communications system uses many channels, the size and cost reduction of the filter is very important because the same number of filters as the number of channels are used.
As the filter used in the wireless communications system, there are filters using a lumped element, a micro-strip or a strip line filter using a transmission line, a resonator filter, a wave guide filter, and a SAW (surface acoustic wave) filter and so forth.
Among the various filters as described above, the cavity resonator filter loaded by dielectric material shows a high quality factor, and its mass and volume are relatively small compared with cavity filters without dielectric material.
The cavity resonator filter must have an appropriate number of resonators and a required connectivity to realize a preferable frequency response characteristic. In general, since the number of resonators constituting the filter must be high to realize a filter with a sharp roll-off rejection characteristic, the size of the filter gets large. Accordingly, to provide a small-size filter, methods of reducing the size of the resonator itself and the number of resonators have been undertaken by using a cavity resonator of a dual mode or a triple mode in which several resonance modes are realized in one cavity.
As high quality wireless system performance is required, a filter having stringent performance has been required. However, as the frequency response characteristic is very sensitive errors can occur when realizing the filter, such as distortion of the frequency characteristic due to a design error or a manufacturing error directly affects the performance of the filter. Therefore, there is a case that the performance requirements of the filter are not satisfied due to a small error.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.